Over the past 25 centuries, orthodontists have been engaged in the process of repositioning teeth from faulty arrangements, or “malocclusions,” into healthier and more esthetic arrangements. In order to move teeth, three elements are generally required: 1) force, 2) time and 3) space. The mouth responds to a sustained force placed on a tooth by rearranging, or “remodeling,” the alveolar bone around the root of the tooth. Particularly, osteoclasts break down bone in the area where the tooth is being moved to in order to create space for the tooth. As a result, the tooth is able to move in the direction of the force applied thereto. Additionally, osteoblasts form new bone tissue in the area where the tooth is being moved from.
In further detail, FIGS. 1A-1B illustrate a “remodeling” of the alveolar bone. As illustrated in FIG. 1A, a tooth is comprised of a crown 0 and a root 1. The crown is visible in the mouth, while the root is not, because it is encased in soft connective tissue fibrous mesh known as the periodontal ligament (PDL) 3, and PDL 3 is surrounded by alveolar bone 4. Alveolar bone 4 faces PDL 3 on one side, and is covered by gingival and mucosal tissue (gum) 5 on the other. PDL 3, alveolar bone 4 and gum 5 contain living cells which are responsible for the remodeling of all these tissues in response to orthodontic forces. This remodeling process is the mechanism that facilitates orthodontic tooth movement. The cells are attached to the matrix that surrounds them, and when they become subjected to orthodontic forces that stretch or compress them, the strain is transmitted directly to the cell nucleus and nucleolus, activating the production of multiple molecules including membrane receptors, which interact with signal molecules derived from the nervous, immune, vascular and skeletal systems.
As illustrated in FIG. 1B, physical changes result from application of an orthodontic force to crown 0 of the tooth. The mechanical forces and moments are applied to affect the desired type of tooth movement. Accordingly, a tooth may be extruded, intruded, rotated, tipped, or translated. FIG. 1B illustrates a translatory movement which results from a translational force 7 and a rotation 6 of crown 0 around a center of rotation, or fulcrum, located near the apex of root 1. In order to insure a translatory movement, a force couple is created opposite to rotational force 6. This force couple (generated by the interaction between the bracket and the arch wire for braces, and attachments and aligners for aligner devices) creates a moment that moves root 1 along with crown 0 extending the center of rotation from the apex to infinity. Translational force 7 pushes root 1 against alveolar bone 4, opposite to the point of force application, compressing a portion 9 of PDL 3. Likewise, on the side of the tooth where force 7 is being applied, a portion 8 of PDL 3 is being stretched. Root 1 is displaced within the tooth socket of alveolar bone 4, and the PDL 3 responds by widening portion 8 and compressing portion 9. The compressed portion 9 undergoes removal (resorption), while in the stretched portion 8 new layers of bone are deposited on the surface of the old alveolar bone 4. Over time, alveolar bone 4 remodels, allowing the tooth to assume a new position in the place that translational force 7 caused it to move. This remodeling is a direct result of, and consistent with, the compression/resorption and stretching/deposition activity in PDL 3 and juxtaposed alveolar bone 4. When alveolar bone 4 is pressed upon, as occurs when translational force 7 presses on a tooth and PDL 3 compresses, a short-lived electrical spike can be measured across alveolar bone's 4 matrix. This is known as a piezoelectric effect, characterized by the negative side of the potential being detected on the concave side of the flexed bone and the positive side of the potential being detected on the convex side. In addition, the mechanical stress causes movement of tissue fluids. These fluids contain electrical charges that change the cellular electric polarity, stimulating the cells to remodel their surrounding matrices. These stress-generated streaming potentials (SGP) last about 20-30 minutes. When the bone is held in a flexed state, the concave side experiences bone deposition and the convex side experiences bone resorption. As long as the bone remains flexed, this process continues over time until the previously flexed bone appears unflexed or straight.
Over the years, orthodontists have invented devices, generally referred to as “appliances”, that allow clinicians to deliver sustained forces to the teeth. Braces, or “orthodontic brackets and arch wires,” are the classic appliances that most, if not all orthodontists use. These forces are applied to the crowns of the teeth, then transferred to the dental roots, and from there to the tissues that surround the roots, consisting of the periodontal ligament, a thin soft tissue sleeve that embraces each root, separating it from the surrounding alveolar bone. On the outside, the alveolar bone is covered by the gum. All these tissues must remodel, in order to enable the orthodontically treated teeth to move to new positions in the jaw. Braces consist of small brackets that are glued, or “bonded,” to the crowns of teeth, and a wire is then inserted into slots in the brackets and held in place with a ligature or clip. The brackets do not generate forces themselves, but rather transfer forces to the teeth from the deflected wire, when it is inserted into the slot in the bracket and held in place by the ligature. The wire has a “memory,” i.e., a characteristic by which the wire tends to return to its original shape, and in doing so, exerts a force on the bracket that is in turn transmitted to the tooth. Through the application of various types, shapes and sizes of wires, the teeth eventually align themselves into the desired position in the dental arch. The technical term used among orthodontists to describe braces is “comprehensive fixed appliance”. The tooth movement is clarified by Wolff's Law, which states, in effect, that bone under mechanical stress is remodeled to accommodate and reduce the stress.
Bone cells are responsive to various physical and chemical agents, amongst them: mechanical force and electricity. When direct current, in the order of 20 μA, is applied to bone, deposition of new bone matrix occurs near the cathode, while destruction of old bone is found near the anode. This feature, as well as the ability of bone cells to respond simultaneously to force and electricity, create a favorable environment for acceleration of the rate of bone remodeling and, consequently, the speed of tooth movement. Due to a synergistic relationship between applied force and applied electricity, when both force and electricity are applied simultaneously less of each are necessary to achieve an optimally enhanced osteogenic response from the bone.
Typical orthodontic appliances must be worn by the patient for extended periods of time, often several years or more, in order to achieve the desired results. The classic orthodontic treatment that requires the continuous application of forces to attain the planned tooth movement is expensive, as it requires frequent modifications of the magnitude and direction of forces applied to different teeth, to achieve the necessary progress, requiring frequent adjustments by the treating orthodontist. Moreover, wearing the mechanical fixtures known as “braces” creates a considerable discomfort for the patient, and at the same time this condition will cause an aesthetic concern to the patient as the metallic fixtures (Braces) are visible to other people. In addition, the braces promote the accumulation of bacteria and viruses, harmful to the teeth and their surrounding tissues.
In order to overcome some of the above disadvantages, orthodontic appliances have been developed that can be inserted and removed by the patient, and worn part-time. A myriad of removable appliances have been developed over the years, but the vast majority are not “comprehensive” in nature, i.e. the removable appliances address specific movements or malocclusions, and are only used for a certain limited period of time. Treatment with removable appliances is often used in conjunction with braces or other appliances. The wish to shorten the duration of orthodontic treatment is universal, for obvious reasons. It has led to the development of surgical procedures, which are invasive in nature, and aimed at causing wide-spread inflammation and wound healing, leading to rapid tooth movement.
U.S. Pat. No. 4,153,060, issued on May 8, 1979 to Korostoff et al., the entire contents of which are incorporated herein by reference, teaches a method and apparatus for electrically stimulating alveolar bone remodeling and tooth movement in the mouths of humans. A positive electrode is placed on the gum surface adjacent the bone structure which is to be resorbed. A negative electrode is placed on the gum surface adjacent the bone tissue which is to be accreted or built up. A current source is connected, such that a small current flows between the electrodes, which have the effect of stimulating bone growth in a specific direction. In a particular arrangement, the electrodes are placed on the gum surface adjacent a tooth, the positive electrode on the side towards which the tooth should move, and the negative on the side from which the tooth will move. Application of a small current to the electrodes will enhance the repositioning of the tooth in conjunction with normal orthodontic practices. However, Korostoff fails to provide a comprehensive and effective system for reducing orthodontic treatment time. Additionally, the electrodes of Korostoff tend to cause excessive irritation of the gums. Although several decades have passed, the method of Korostoff has not achieved wide use by orthodontists.
U.S. Pat. No. 4,854,865, issued Aug. 8, 1989 to Beard et al., teaches an improved method of orthodontic electro-osteogenesis using a biocompatible anode in contact with an electrolytic gel between the anode and epithelial gingiva at an area of osteoclastic or osteoblastic activity, and a biocompatible cathode in contact with a different type of electrolytic gel between the cathode and epithelial gingiva at an area of osteoclastic or osteoblastic activity. Current is then applied across the anode and cathode to stimulate osteogenesis. This method stimulates osteogenesis, which is an important element in tooth movement, but is unable to demonstrate how to achieve desirable results, or to enable to complete orthodontic treatment in a shorter amount of time.
U.S. patent application publication US 2014/0023983, published Jan. 23, 2014 to Lowe et al., the entire contents of which is incorporated herein by reference, is addressed to an electro-orthodontic appliance which helps accelerate orthodontic tooth movement through the application of a controlled electric current to gum and teeth, thus stimulating osteogenesis. Lowe does not provide a comprehensive solution for enhancing orthodontic tooth movement in a plurality of treatment situations, including a combination of bodily and tipping movements of a plurality of teeth. Additionally, the system of Lowe evokes root resorption due to stimulation of cells residing on the surface of the dental root, which is undesirable.
U.S. patent application publication US 2009/0117513, published May 7, 2009 to Nemeh et al., the entire contents of which is incorporated herein by reference, is addressed to a method and apparatus for concurrent treatment of multiple oral diseases and defects while promoting general oral hygiene utilizing direct current electricity applied to the gingival tissues of the mouth. Nemeh does not provide a system or method of utilizing this electricity for improvement of orthodontic treatment. It is therefore an object of the present disclosure to overcome at least part of the disadvantages of the prior art.